The present invention relates generally to skates and, in particular, to a skate frame having a core of lightweight material to increase structural strength-to-weight and stiffness-to-weight ratio of the frame.
In-line roller skates generally include an upper shoe portion having a base secured to a frame that carries a plurality of longitudinally aligned wheels. The upper shoe portion provides the support for the skater""s foot, while the frame attaches the wheels to the upper shoe portion. Because in-line skates are designed to accommodate a variety of skating styles, including high-performance competitions, it is desirable for such skate frames to be lightweight, stiff, and strong. Skate frames may be constructed from a variety of materials, including aluminum, injection molded plastic, and composites. Although aluminum skate frames are structurally strong and stiff, they are expensive. Skate frames constructed from an injection-molded plastic are often reinforced with short, discontinuous fibers. Although such skate frames are lower in cost than aluminum frames, they lack the specific strength and stiffness performance characteristics associated with continuous fiber-reinforced composite frames.
Currently, fibers of glass or carbon are preferred to reinforce composite frames. Glass reinforced composite skate frames are both structurally stiff and strong, but they are heavier than composite frames reinforced with carbon fibers. Although carbon fiber reinforced skate frames are lightweight, strong, and stiff, they are expensive.
Frames constructed from composites reinforced with glass, carbon fibers, or other high performance fibers, may be improved by sandwiching a core material between face sheets or skins of reinforced composite material. The core is a lighter, less expensive material with moderate structural properties in terms of strength and stiffness.
Prior in-line skate frames having a core construction include inverted U-shaped skate frames having a polymer core bonded within the concave portion of the skate frame. In such skate frames, the core is positioned between the frame""s arcuate portion and the wheels. Although such skate frames provide increased structural stiffness, the core is subjected to accelerated wear and damage because it is exposed directly to the wheels and road debris. Therefore, such a skate frame may have a shortened useful life.
Other attempts of providing an in-line skate frame with a core include inverted U-shaped skate frames with core material sandwiched between two composite face sheets. In this type of frame, the core extends from below the wheel attachment points upwardly and across the upper surface of the frame. The wheels and shoe portion of the skate are attached to the frame by drilling or molding their respective attachment points through the sandwich construction, thereby subjecting the core material directly to the loads of both the wheel axle and shoe portion attachment bolts. This construction is undesirable because the core material is in direct contact with the wheel and shoe attachment hardware and, therefore, is susceptible to breakage.
Still other attempts of providing in-line skate frames with a core have included a core inserted within the junction between the sole of the shoe portion and the skate frame. Such skate frames have a flange extending laterally from both sides of the upper end of the skate frame, such that the lateral and medial sides of the upper surface span outwardly to cup the sole of the shoe portion therein. The interior of the flange portion is filled with a core material to absorb a portion of the loads associated with traversing a surface. The location of the flanges relative to the frame is custom made to accommodate a particular skater""s foot and shoe width. Because the flange portion is sized to cup a specific shoe width, there is limited adjustment of the location of the shoe portion relative to the frame. Therefore, such a skate frame is not very robust in accommodating different skating styles, even for the skater for whom the skate was custom made. Moreover, because the skate is custom made and designed for a particular skater, it is expensive to manufacture.
Thus, there exists a need for a composite in-line skate frame having a lightweight core that not only maintains the frame""s strength and stiffness, but also is economical to manufacture, and meets the performance expectations of a skater.
The present invention provides both a skate frame for an in-line skate having an increased structural strength-to-weight ratio, and a method of constructing such a frame. The in-line skate has a shoe portion and a plurality of longitudinally aligned wheels capable of traversing a surface. The skate frame includes first and second sidewalls and a shoe mounting portion. Preferably, the sidewalls and shoe mounting portion include skins constructed from a material having a first average density. Each of the sidewalls has an upper end and a lower end. The lower ends of the sidewalls include wheel load introduction portions, wherein loads associated with the wheels are transferred to the sidewalls. The upper ends of the sidewalls are held in spaced parallel disposition by the shoe mounting portion spanning therebetween. The shoe mounting portion includes a shoe load introduction portion, wherein loads associated with the shoe portion are transferred to the shoe mounting portion. The skate frame also includes core material disposed within at least the first and second sidewalls, or within the shoe mounting portion. The core material is removed from at least the wheel and shoe load introduction portions.
In an aspect of a skate frame constructed in accordance with the present invention, the core material has a second average density that is less than the material density of the skins of both the sidewalls and shoe mounting portion by a predetermined amount and has predetermined structural properties. The core material occupies a volume within the skate frame to provide the skate frame with an increased structural strength-to-weight ratio.
In an aspect of the first preferred embodiment of the present invention, the core material is positioned within sidewalls. The core material is chosen from a group of materials that includes both reinforced and unreinforced polymers and natural materials.
In another aspect of the first preferred embodiment of the present invention, the skate frame also includes a plug of filler material disposed between the core material and the load introduction portions to absorb at least a portion of the loads associated with the wheels and shoe portion.
In yet another aspect of the present invention, the core material defines a varying height along a longitudinal axis extending between the ends of the skate frame.
In an alternate embodiment of the present invention, core material is disposed within the shoe mounting portion.
In yet another alternate embodiment of the present invention, core material is disposed within both the first and second sidewalls and the shoe mounting portion.
A method of constructing a skate frame for an in-line skate is also provided. The method includes the steps of forming a U-shaped first skin and positioning core material at a predetermined location on the first skin. The method further includes the step of forming a U-shaped second skin over the first skin, such that the core material is positioned and sealed between the first and second skins. A plug of filler material is disposed between the first and second skins to absorb at least a portion of the loads associated with at least the wheels or shoe portion of the skate. Finally, the method includes the step of curing the frame.
The skate frame of the present invention provides several advantages over skate frames currently available in the art. The skate frame of the present invention is lighter than solid composite or aluminum frames because a lightweight core material occupies a substantial volume within the frame. Also, because the core material is lightweight and provides a distance of separation between the skins of the sidewall, the strength-to-weight ratio of the frame is increased. Further, because the skate frame utilizes a core material that is less expensive than the reinforced composite material it replaces, it is more cost efficient than skate frames having an all composite construction. Finally, because the core material is removed from the load introduction points associated with the wheels and shoe portion, the skate frame has a longer useful life than skate frames having a core that is in direct contact with the load introduction points. Thus, a skate frame constructed in accordance with the present invention has an increased strength-to-weight ratio and is less expensive than those currently available in the art.
In another embodiment, for each wheel a threaded insert is embedded in the core material in the lateral sidewall with the threaded portion extending into the channel between the first and second sidewall. A tubular insert is installed in the medial sidewall, in axial alignment with the threaded insert, such that a threaded axle can be inserted through the threaded insert and the wheel, to engage the threaded insert, thereby rotatably attaching the wheel to the frame.